Bluff body turbine

ABSTRACT

A passive bluff body is disposed in flowing fluid for generating power. The shape of the bluff body supports a predetermined oscillatory clockwise and counter clockwise movement about a pivot absent the influence of electrical or mechanical devices for biasing the bluff body&#39;s motion for a given velocity, or range of velocities, of the fluid flow.

FIELD OF THE INVENTION

The invention relates to power generation and more particularly to bluffbody power generation.

BACKGROUND

In power generation creating power from renewable resources is a growingindustry. As the global population increases, so does the need for morepower. Existing power systems struggle to meet the demand of theircustomers. Our environmentally conscious society, while demanding morepower, also desires clean renewable sources of energy. Whilehydro-electric power is generated via a renewable resource, water, theeffects on the environment can be devastating. Damming a river causesflooding of large areas of land, destroying the natural environment ofthe local area. Fish populations can be impacted if fish cannot migrateupstream to spawning grounds or if they cannot migrate downstream to theocean.

Development of other power generating technologies have emerged from thedesire for renewable energy sources, for example, the sun. Solar energyis an attractive renewable resource however, there are severaldisadvantages associated with implementing a solar energy system. Solarpanels are expensive to purchase and costly to maintain. Installation isa challenge as a large area is needed to install the panels. Also,harnessing solar power is not ideal in northern climes where there arefew hours of sunlight.

Wind farms have emerged as another method for harnessing power from arenewable resource. Large numbers of wind turbines are placed on top ofhills to maximize wind flow and are prominent along the horizon,consequently they are often viewed as eyesores. Other disadvantagesinclude intruding on birds' migrational flight paths, as they pose arisk to birds flying between the turbine blades. Also, those living nearwind farms are exposed to noise which is intrusive and out of place inthe country side where they are often located.

The use of bluff bodies in air or water to generate electricity isanother example of a harnessing the power of renewable source of energy.In U.S. Pat. No. 7,224,077 B2, “Bluff Body Energy Converter”, forexample, a bluff body mounted for rotation is disposed in a streamperpendicular to the oncoming flow. Vortices that occur about the bluffbody cause it to move and an impedance matching system is employed forvarying the natural frequency characteristics of the bluff body, suchthat it oscillates—moves back and forth—at a frequency. The disclosedbluff body energy converter comprises a complex feedback system todetermine when the natural frequency characteristics of the bluff bodychange. Also, such a complex system often requires regular maintenanceand calibration.

It would be advantageous to overcome some of the disadvantages of theprior art.

SUMMARY OF THE INVENTION

In accordance with an embodiment of the invention there is provided amethod of generating electric current comprising providing an apparatuscomprising a pivot, a generator, a first part and a second part, thefirst part for pivoting relative to the second part about the pivot, thegenerator for generating electric current in response to relative motionabout the pivot between the first part and the second part and disposingthe first part within a fluid flow, the first part shaped for, inresponse to the fluid flow, oscillating in alternating directions in apredetermined fashion.

In accordance with an embodiment of the invention there is provided anapparatus for generating electric current comprising a pivot, a bluffbody comprising a vortex inducing feature and shaped for when disposedin a flowing fluid with velocity v1 having a predetermined oscillatingmovement of the bluff body in alternating directions about the pivotinduced for resulting in relative motion therebetween, and a generatorcoupled between the pivot and bluff body for generating electric currentin response to the relative motion.

In accordance with an embodiment of the invention there is provided anapparatus for generating electric current comprising a pivot, a threedimensional triangular shaped bluff body comprising: a first sidewalland a second sidewall coupled together at an apex for being directedinto the fluid flow, an opening for mating with the pivot for supportingrotation of the bluff body thereabout, a back wall, a second roundedcorner opposite the apex and between the first sidewall and the backwall, a third corner opposite the apex and between the second sidewalland the back wall, for when disposed in a flowing fluid with velocity v1resulting in vortex shedding for inducing a predetermined oscillatingmovement about the pivot for resulting in relative motion between thepivot and the bluff body; and a generator coupled between the pivot andthe bluff body for generating electric current in response to therelative motion.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the invention will become more apparentfrom the following detailed description of the preferred embodiment(s)with reference to the attached figures, wherein:

FIG. 1 a is a top view of a bluff body turbine having a general wedgeshape and having cylindrical vortex inducing features.

FIG. 1 b is a side view of the bluff body turbine of FIG. 1 a.

FIG. 2 a is a top view of a bluff body turbine having a general wedgeshape and having cylindrical vortex inducing features disposed in ariver.

FIG. 2 b is a side view of the bluff body turbine of FIG. 2 a mountedonto a riverbed.

FIG. 2 c is a top view of a bluff body turbine having a general wedgeshape and having cylindrical vortex inducing features disposed in ariver and showing water disturbance about the bluff body.

FIG. 2 d is a top view of a bluff body turbine having a general wedgeshape and having cylindrical vortex inducing features disposed in ariver and showing motion due to the force of the river and vortexformation.

FIG. 2 e is a top view of a bluff body turbine having a general wedgeshape and having cylindrical vortex inducing features disposed in ariver and showing shedding vortices for moving in a first direction.

FIG. 2 f is a top view of a bluff body turbine having a general wedgeshape and having cylindrical vortex inducing features disposed in ariver and showing shedding vortices for moving in a second otherdirection.

FIG. 3 a is a side view of a bluff body turbine having a general wedgeshape and having cylindrical vortex inducing features disposed in anocean comprising a rotor and stator for power generation.

FIG. 3 b is a top view of the bluff body turbine of FIG. 3 a.

FIG. 4 a shows an exemplary vortex inducing feature.

FIG. 4 b shows another exemplary vortex inducing feature.

FIG. 4 c shows another exemplary vortex inducing feature.

FIG. 4 d shows another exemplary vortex inducing feature.

FIG. 5 a is a side view of a bluff body turbine comprising a pluralityof bluff bodies, each designed for a different fluid flow rate.

FIG. 5 b is a top view of the bluff body turbine of FIG. 5 a.

FIG. 6 a is a side view of a bluff body turbine comprising a pluralityof bluff bodies, each designed for a same fluid flow rate.

FIG. 6 b is a top view of the bluff body turbine of FIG. 6 a.

FIG. 7 a shows a top view of a bluff body turbine having a modifiableshape for tuning operation thereof, shaped in a first shape.

FIG. 7 b shows a top view of a bluff body turbine having a modifiableshape for tuning operation thereof, shaped in a second shape.

FIG. 7 c shows a top view of a bluff body turbine having a modifiableshape for tuning operation thereof, shaped in a third shape.

FIG. 8 shows a bluff body turbine wherein the power generation throughrelative motion about a pivot is a pivot at which the bluff body turbineis other than supported.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The following description is presented to enable a person skilled in theart to make and use the invention, and is provided in the context of aparticular application and its requirements. Various modifications tothe disclosed embodiments will be readily apparent to those skilled inthe art, and the general principles defined herein may be applied toother embodiments and applications without departing from the scope ofthe invention. Thus, the present invention is not intended to be limitedto the embodiments disclosed, but is to be accorded the widest scopeconsistent with the principles and features disclosed herein.

Vortices are formed when fluid flows past a blunt object. These vorticeshave an ability to bias the blunt object.

Vortex shedding is caused when a fluid flowing past a blunt objectcreates alternating low pressure zones on the downstream side of theblunt object. Vortex shedding is a problem that needs addressing, forexample in chimney design as when the fluid flow is at a criticalvelocity, the vortex shedding results in a resonant oscillation.

A bluff body is an object that produces resistance when immersed in amoving fluid. A region of separated flow occurs over a large portion ofthe surface resulting in vortex formation proximate a vortex inducingfeature thereof.

A vortex inducing feature is a feature within a bluff body shaped forinducing a predictable vortex proximate the vortex inducing feature whenthe bluff body is in a first position relative to the fluid flow, thepredictable vortex for biasing the bluff body to move in a predetermineddirection.

A line is curved when it deviates from straightness in a smooth,continuous fashion.

Shown in FIG. 1 a is a bluff body turbine (BBT) according to anembodiment of the invention. BBT 100 comprises a bluff body 101, a pivot102 and a power generator, for example a stator 107 and a rotor 106.Bluff body 101 freely rotates 360° about pivot 102, which is in anapproximately fixed position. Rotor 106 is coupled to bluff body 101,and stator 107 is coupled to pivot 102, such that in use rotor 106 movesrotationally about stator 107 as bluff body 101 moves about pivot 102.The relative motion between stator 107 and rotor 106 is used to generateelectric current. Bluff body 101 comprises sidewalls 103 a-b and vortexinducing features in the form of cylinders 104 a-b, located at theopposite end of sidewalls 103 a-b from pivot 102 along the length ofbluff body 101 parallel to the y-axis. Sidewall 103 a faces in a firstdirection and sidewall 103 b faces in an approximately opposing seconddirection.

In FIG. 1 a, bluff body 101 is fabricated from a single piece ofmaterial. Sidewalls 103 a-b and cylinders 104 a-b are integrally formed.Construction material of bluff body 101 is rigid and water resistant forother than absorbing significant proportions of the forces of the fluidflow, for enhanced movement of bluff body 101 as forces from the fluidflow act on BBT 100. An example of a bluff body construction material ishard plastic. Also, a bluff body is constructed from material strongenough to endure forces exerted by the fluid flow. The materialsdescribed are water resistant as the bluff body of the presentembodiment is for being disposed in bodies of water or exposed to rain.BBT 100 is an open body, however, rotor 106 and stator 107 are protectedfrom the elements. For example, rotor 106 and stator 107 are encased inwaterproof materials, are sealed against water damage, or alternativelyare designed of materials for use in water. Alternatively, a bluff bodyis other than water resistant. For example, the necessity for a waterresistant material is reduced when a BBT is for use in thermal airdrafts. Of course, material selection is dependent upon an intended usefor a bluff body and the present exemplary materials are merelysuggestive. Another exemplary construction material of the bluff body ismetal, for example steel, covered with a coating to protect the bluffbody from the elements.

As shown in FIG. 1 a and FIG. 1 b, BBT 100 comprises vortex inducingfeatures in the form of cylinders disposed with an axis of rotationalong the depth of bluff body 101 (z-axis). Cylinders 104 a-b are shownhollow though this need not be the case. The exterior walls of bothsidewalls, 103 a and 103 b, including the cylinders 104 a and 104 bcomprise a rough surface. A specific and non-limiting example of a roughsurface is abrasive grinding paper, for example ANSI 60 grit (250 to 300μm). Alternatively, the construction material is a metal and both thesidewalls are made abrasive, for example via sandblasting.Alternatively, the rough surface is implemented for enhancing theeffects of the fluid flow in vortex creation and/or in responsiveness tovortices so created. Also, the absence of a back wall increases alikelihood of the vortices to shed. Alternatively, the absence of arough surface on the back wall increases a likelihood of the vortices toshed.

Alternatively, bluff body 101 is restricted in its rotation about theaxis of rotation. Alternatively, bluff body 101 is a closed body whereincorners 104 a and 104 b are connected via a third wall (not shown.)Further alternatively, BBT 100 is completely closed with a wall on thetop and bottom of the bluff body allowing the pivot to pass through achannel through the bluff body. Alternatively, bluff body 101 isfabricated from plural pieces of material. Alternatively, vortexinducing features are other than cylindrical. Alternatively, the bluffbody proximate the pivot point is one of pointed, rounded, andelliptical.

Referring to FIG. 2 a, BBT 100 is disposed in a flowing fluid, forinstance, in a river 200. The directional flow of river 200 is indicatedby arrow 203, along the y-axis, and BBT 100 is disposed in river 200 ina downstream position. In the specific example shown in FIG. 2 b, pivot102 is mounted to the river bed 201 of river 200, such that the force ofthe water flow substantially other than causes pivot 102 to rotate.Alternatively, the pivot 102 is attached to a fixed structure such thatthe force of the water flow other than causes pivot 102 to substantiallyrotate. Bluff body 101 is approximately neutrally buoyant and is free torotate 360° about pivot 102 as indicated by arrow 202. Bluff body 101 isalso disposed underneath the water's surface at such an elevation as tonot interfere with boats, ice formation, etc. As water flows pastcylinders 104 a and 104 b of bluff body 101, vortices 204 a and 204 bform and shed proximate cylinders 104 a and 104 b, as shown in FIG. 2 c.Alternatively, BBT 100 is disposed in a flowing fluid such as an oceanor a lake. Alternatively, BBT 100 floats on top of the water. Furtheralternatively, the bluff body is supported within the fluid flow by thepivot 102.

In the art of fluid dynamics, vortex formation and shedding is a knownphenomenon and the forces generated are known to randomly bias bluffbodies in response thereto. Vortex shedding is a particular instancewherein the forces alternate resulting in a body oscillating frequentlyundesirably so. According to an embodiment of the invention a bluff bodyturbine is provided comprising known vortex inducing features, disposedin a flowing fluid, for passively maintaining an oscillating motion at agiven fluid flow rate. Referring to FIG. 2 d, shown is BBT 100. In thisexample, cylinders 104 a and 104 b have a diameter, d1. Diameter d1 isselected to optimize displacement of bluff body 101 for a known waterflow rate, for example velocity V, of river 200. The water flowing alongsidewall 103 b, as indicated by arrow 205, causes bluff body 101 topivot clockwise aiding in the formation of vortex 204 a near cylinder104 a. Bluff body 101 moves towards the low pressure region caused byvortex 204 a and, in conjunction with the force of the water pushing onsidewall 103 b, bluff body 101 pivots clockwise.

A natural balance of forces occurs between vortex 204 a and the force ofwater pushing sidewall 103 a. The force of the water acts to stop thebluff body 101 in motion and causes the shedding of vortex 204 aspatially proximate to cylinder 104 a. As vortex 204 a is shed, theforce of the river water pushes on sidewall 103 a, as indicated by arrow206, and vortex 204 b forms as shown in FIG. 2 e. Bluff body 101 movestowards the low pressure region caused by vortex 204 b and the force ofthe river water pushes on sidewall 103 a aiding the movement of bluffbody 101 to pivot counter-clockwise. The force of the river water, asindicated by arrow 207 acts to stop motion of the bluff body 101 andaids in shedding vortex 204 b spatially proximate to cylinder 104 b, asshown in FIG. 2 f. The alternating formation of vortices 204 a and 204b—vortex shedding—causes bluff body 101 to oscillate—moving inalternating directions about the pivot. The relative motion betweenstator 107 and rotor 106 is used to generate electricity.

Exterior wall of sidewalls 103 a and 103 b and cylinders 104 a-bcomprise a rough surface for supporting formation of vortices 204 a and204 b. A rough surface on the exterior walls of sidewalls 103 a and 103b and cylinders 104 a-b increases a likelihood of the vortices to form.Also, the absence of a back wall increases a likelihood of the vorticesto shed. Alternatively, the absence of a rough surface on the back wallincreases a likelihood of the vortices to shed. It is the formation andshedding of vortices that results in BBT 100 oscillation back and forth.

For known velocity V of river 200, diameter d1 is selected for cylinders104 a and 104 b for forming vortices that bias the bluff bodyappropriately and such that the distance travelled by the bluff bodyalong the x-axis is predictable and optionally optimized. In thisspecific and non-limiting example, the distance travelled by bluff body101 is 1.7 times d1.

Bluff body 101 freely rotates 360° about pivot 102 allowing theharnessing of energy from the natural uneven movement of the flowingmedium as well as the natural change in direction of the flow. BBT 100'sdesign permits the uneven action of a natural flowing fluid to swing theBBT into whatever path the flowing fluid takes. The swinging motionabout the pivot 102 results from formation and shedding of vorticeswhether they be in oscillation or not and from the fluid flow direction.Any force acting upon BBT 100 causing clockwise or counter clockwisemotion causes the relative motion between the stator 107 and rotor 106resulting in generating electricity.

Advantageously, selection of the diameter d1 allows for a passive bluffbody implementation lacking any impedance matching or other mechanicalbiasing as the vortices form and shed in an alternating fashion for, inthe absence of any external control, resulting in electricitygeneration. Such a passive bluff body is advantageous both due to itssimplicity of manufacture and due to its simplicity of installation anduse. Further, the geometry shown results in controlled vortex sheddingthat does not present a danger to the bluff body.

Referring to FIG. 3, shown is a BBT disposed in a flowing fluid, forexample, an ocean 308. BBT 300 comprises a bluff body 301 and a pivot302. The top of pivot 302 is coupled to a platform in the form of anoilrig 303 by arm 304. Alternatively, BBT 300 is fixed to a wharf, arock, or another structure near or in ocean 308. BBT 300 comprisesdevices for power generation in the form of rotor 306 and stator 305.Bluff body 301 freely rotates 360° about pivot 302, which is in a fixedposition and other than rotates. Rotor 306 is coupled to bluff body 301,and stator 305 is coupled to pivot 302, such that in use, rotor 306moves rotationally about stator 305 as bluff body 301 moves about pivot302. The relative motion between stator 305 and rotor 306 generateselectric current that is provided to oilrig 303 via electrical cable307. Alternatively, the power generation devices comprise two otherparts and the relative motion between the two parts generateselectricity.

Bluff body 301 comprises sidewalls 309 a-b and vortex inducing featuresin the form half cylinders 308 a-b. Half cylinders 308 a-b are locatedat the opposite end of sidewalls 309 a-b from pivot 302 along the lengthof bluff body 301, parallel to the y-axis. Sidewall 309 a is facing in afirst direction and sidewall 309 b is facing in an approximatelyopposing second direction. The shape of bluff body 300 is designed tooptimize the energy transfer from oceanic current forces to the electricpower generation device for a known current velocity, v2, in ocean 308near oilrig 303. Half cylinders 308 a-b each have a diameter d1.Diameter d1 is selected to optimize the displacement of bluff body 301for velocity v2. As forces of the current flow against bluff body 301,half cylinders 308 a-b contribute to formation and shedding of vorticescausing bluff body 301 to move about pivot 302 in an oscillating manner.For known current velocity v2, the distance travelled by bluff body 301along the x-axis is 1.7 times diameter d1. Optionally, d1 is selected tooptimize the distance travelled along the x-axis for a range ofvelocities, for example v1-v4. Alternatively, BBT 300 is coupled tooilrig 303 via an arm attached to the bottom of pivot 302.Alternatively, the end of the bluff body disposed into the fluid flow isone of a point, round, and elliptical.

Alternatively, the diameter of half-cylinder 308 a is different than thediameter of half-cylinder 308 b. BBT 300 is optimized for two fluid flowrates, one for 308 a and 308 b.

Shown in FIGS. 4 b-c, BBTs 405 and 406 comprise vortex inducingfeatures. Alternatively, vortex inducing features are other thanenclosed shapes. For example, shown in FIG. 4 a is BBT 400 in the shapeof a golden spiral comprising vortex inducing features 404 a-b.

Shown in FIG. 4 a is a bluff body turbine comprising pivot 402 and abluff body 401 comprising sidewalls 403 a-b and vortex inducing features404 a-b. Sidewall 403 a and vortex inducing feature 404 a form a firstgolden spiral facing in a first direction. Sidewall 403 b and vortexinducing feature 404 b form a second golden spiral facing in anapproximately opposing second direction. Bluff body 401 freely rotates360° about pivot 402, which is in a fixed position and other thanrotates. BBT 400 also comprises devices for power generation (not shown)in the form of a rotor and stator. The rotor is coupled to bluff body401, and the stator is coupled to pivot 402, such that in use, the rotormoves rotationally about the stator as bluff body 401 moves about pivot402. The relative motion between the stator and the rotor generateselectric current.

BBT 400 is designed to optimize the energy transfer from fluid flowforces to the electric power generation device for a known fluid flowrate, for example, v2. Bluff body 401 is shaped to cause and maintain anoscillatory formation and shedding of vortices causing bluff body 401 tomove about pivot 402 in a substantially consistent oscillating mannerfor a known fluid flow rate, v2. Disposed in a flowing fluid moving atvelocity v2, vortices form alternately on both sides of bluff body401—vortex shedding—causing it to oscillate in a clockwise and counterclockwise rotation.

Referring to FIGS. 4 b-4 d, shown are BBT 405-407, respectively. Thebluff body shape for each of bluff bodies 405 b-407 b is shaped to causeand maintain an oscillatory formation and shedding of vortices causingbluff bodies 405 b-407 b to move about pivots 405 a-407 a, respectively,in a substantially consistent oscillatory manner for a known fluid flowrate, v2. Disposed in a flowing fluid moving at velocity v2, vorticesfrom bluff bodies 405 b-407 b cause adjacent bluff bodies to movealternately in a clockwise and counter clockwise rotation.

According to an embodiment of the invention, a BBT comprises a pluralityof vortex inducing features in the form of curved corners having adiameter d, for example as defined by the Strouhal number. The vortexshedding frequency of any bluff body is defined by the Strouhal numberof the flow. The Strouhal number represents the non-dimensional vortexshedding frequency defined as St=fD/U where D is the dimension of thebluff body perpendicular to the oncoming flow, U is the flow speed and fis the vortex shedding frequency. If the diameter of the bluff bodycorner is constant and the speed of the flow increases then thefrequency of vortex shedding decreases and thus the energy outputdecreases when the flow exceeds a flow for the diameter of the bluffbody corners.

Shown in FIG. 5 a and FIG. 5 b is a BBT according to an embodiment ofthe invention. BBT 500 is disposed in a flowing fluid, for example river507, and comprises a plurality of bluff bodies of various diameters andpivot 506. Bluff bodies 501-504 are disposed vertically along pivot 506and are free to rotate 360° around pivot 506 which is mounted to theriver bed 508 of river 507, such that the force of the water flowsubstantially other than causes pivot 506 to rotate. Alternatively, thepivot 506 is attached to a fixed structure such that the force of thewater flow substantially other than causes pivot 506 to rotate. In thisexample, bluff bodies 501-504 are other than attached to one another androtate about pivot 506 independently. BBT 500 also comprises powergenerators (not shown) in the form of rotors and stators. A rotor iscoupled to each of the bluff bodies 501-504, and a stator is coupled topivot 508 near each rotor, such that in use, a rotor moves rotationallyabout a stator as bluff bodies 501-504 moves about pivot 506. Therelative motion between each stator and rotor generates electriccurrent. Alternatively, a stator is attached to each bluff body and arotor is disposed within the pivot 506.

The vortex shedding frequency of any bluff body is defined by theStrouhal number of the fluid flow. The Strouhal number represents thenon-dimensional vortex shedding frequency defined as St=fD/U, where D isthe dimension of the bluff body perpendicular to the oncoming flow, U isthe flow speed and f is the vortex shedding frequency. An increase inthe fluid flow rate, for a bluff body of known diameter, causes thefrequency of vortex shedding to decrease and thus the energy outputdecreases.

For example, BBT 500 is designed to optimize energy transfer from asingle body of water, river 507, of varying fluid flow rates. Each bluffbody 501-504 comprises vortex inducing/shedding shapes in the form ofhalf cylinders, 501 a-b-504 a-b respectively, of varying diameters. Forexample, half cylinders 501 a-b have diameter d1, half cylinders 502 a-bhave diameter d2, and so forth. As the fluid flow rate of river 507increases, the frequency of the vortex shedding decreases. For example,bluff body 501, comprising half cylinders of diameter d1, is designed tooptimize energy transfer from river 507 to BBT 500 for known fluid flowrate f1. River 507 flow rate increases from f1 to f2, wherein f1<f2,reducing the vortex shedding frequency and correspondingly reducing theenergy transfer from river 507 to BBT 500. Bluff body 502, comprisinghalf cylinders of diameter d2, wherein in d1<d2, is designed to optimizeenergy transfer from the river to BBT 500 for known fluid flow rate f2.As river 507 flow rate increases, the diameter of the bluff body mustalso increase to maintain optimal energy transfer from river forces toBBT 500. The shape of bluff bodies 501-504 are designed with halfcylinder diameters d1-d4, respectively, to optimize energy transfer fromthe river forces to BBT 500 for fluid flow rates f1-f4, respectively.Wherein in d1<d2<d3<d4 and f1<f2<f3<f4. In other words, as one range ofStrouhal numbers is exceeded for one diameter the second diameter picksup the next range of Strouhal numbers and continues to shed vortices ata frequency chosen for energy production. Also, as river 507 flow ratedecreases, the diameter of the bluff body optimally also decreases tomaintain optimal energy transfer from river forces to BBT 500.Alternatively, bluff bodies 501-504 are coupled together as a singlebody along the z-axis and only one stator is coupled to pivot 506 andone rotor is coupled to the single body.

Though described hereinabove is a diameter for a particular flow rate,it is understood that by shaping the bluff body in accordance with thepresent embodiment, a single bluff body will oscillate over a range offluid flow rates, though one particular fluid flow rate likely remainsoptimal. Thus, by using four (4) bluff bodies as shown, the range can beextended significantly to encompass a larger range. Alternatively, noncontiguous ranges are used to account for different conditions such asspring, summer, autumn, and winter.

Alternatively, the bluff body is for operation when inserted withinanother fluid flow such as air flow, for example wind.

Shown in FIG. 6 a and FIG. 6 b is a bluff body turbine comprising aplurality of bluff bodies of the same diameters pivoted on a singlepivot for optimizing energy transfer from a single body of water of aconstant range of fluid flow rates. BBT 600 is disposed in river 607 andcomprises pivot 606 mounted to riverbed 608 such that the force of thewater flow substantially other than causes pivot 606 to rotate. Bluffbodies 601-604 are vertically disposed along, and are free to rotate360° about, pivot 606. BBT 600 also comprises power generators (notshown) in the form of rotors and stators. A rotor is coupled to each ofthe bluff bodies 601-604, and a stator is coupled to pivot 606 near eachrotor, such that in use, a rotor moves rotationally about a stator asbluff bodies 601-604 moves about pivot 606. Alternatively, a stator iscoupled to each of the bluff bodies 601-604, and a rotor is coupled topivot 606 near each stator, such that in use, a stator movesrotationally about a rotor as bluff bodies 601-604 moves about pivot606. The relative motion between each stator and rotor generateselectric current.

Referring to FIG. 7, a bluff body turbine comprising adjustablemechanisms for modifying the shape of a bluff body comprised therein isshown. BBT 700 comprises bluff body 702 and pivot 701 about which bluffbody 702 freely rotates. BBT 700 also comprises devices for powergeneration, a first part and a second part (not shown.) The first partis coupled to bluff body 702, and the second part is coupled to pivot701 and in use, the relative motion between the two parts generateselectricity.

The shape of BBT 700 is modifiable via a mechanical mechanism, forexample brace 704 such that it accommodates various fluid flow rates foruse in fluid bodies with varying flow rates. Tuning of the bluff bodyshape to adjust for flow rate changes or to calibrate a bluff body for anew fluid flow avoids electrical and electronic tuning circuits whilesupporting a more near optimum operation. Bluff body 702 constructionmaterial comprises flexible material, for example rubber. Optionally,the bluff body 702 comprises a flexible metallic skeleton.

Alternatively, a back wall of the bluff body of FIG. 7 closes the backof the approximately triangular bluff body and expands and contracts inresponse to tuning of the bluff body shape resulting in a bluff bodyhaving variable diameter rear corners for use in current generation whendisposed within a fluid flow.

Referring to FIG. 8, shown is apparatus 800 comprising a bluff body 801for relatively oscillating about pivot 802. The bluff body 801 need notbe supported by pivot 802 and here, pivot 802 is provided with a fin formaintaining the pivot relative to the oscillating bluff body while thebluff body 801 is supported at 804 by tether 803.

For the embodiments described above, exterior walls of a BBT and vortexinducing features optionally comprise a rough surface which increases alikelihood of vortices to form. Also, the absence of a back wallincreases a likelihood of the vortices to shed. Alternatively, theabsence of a rough surface on the back wall increases a likelihood ofthe vortices to shed. It is the formation and shedding of vortices thatresults in BBT oscillation back and forth.

The embodiments presented are exemplary only and persons skilled in theart would appreciate that variations to the embodiments described abovemay be made without departing from the scope of the invention. The scopeof the invention is solely defined by the appended claims.

What is claimed is:
 1. An apparatus for generating electric currentcomprising: a pivot; a bluff body comprising a vortex inducing featureand shaped for when disposed in a flowing fluid with velocity v1 havinga predetermined oscillating movement of the bluff body in alternatingdirections about the pivot induced for resulting in relative motiontherebetween; and a generator coupled between the pivot and bluff bodyfor generating electric current in response to the relative motion,wherein the vortex inducing feature comprises a first curved shapedcorner between a first sidewall of the bluff body and a side of thebluff body opposite a direction from which the fluid flows, and a secondcurved shaped corner between a second sidewall of the bluff body and theside of the bluff body opposite a direction from which the fluid flows,the bluff body having the first curved shaped corner and the secondcurved shaped corner for resulting in stable vortex shedding whendisposed in a fluid flow of a critical velocity, and wherein the firstcurved shape and the second curved shape comprise a golden spiral. 2.The apparatus according to claim 1 wherein the first curved shape andthe second curved shape each comprise a portion of a different cylinder.3. The apparatus according to claim 1 wherein the pivot is mounted to astationary body for preventing translational movement of the pivot. 4.The apparatus according to claim 1 wherein the apparatus is tethered toa body.
 5. The apparatus according to claim 4 wherein the pivotcomprises a fin for maintaining an orientation of the pivot relative toa fluid flow direction.
 6. The apparatus according to claim 1 whereinvelocity v1 comprises a range of velocities.
 7. The apparatus accordingto claim 5 comprising a plurality of bluff bodies, each of the pluralityof bluff bodies mounted for pivoting about the pivot.
 8. The apparatusaccording to claim 7 wherein the plurality of bluff bodies are attachedto one another in a stacked arrangement.
 9. The apparatus according toclaim 1 absent a control system for modifying the predeterminedoscillating movement of the bluff body.
 10. The apparatus according toclaim 1 absent a feedback system for modifying the predeterminedoscillating movement of the bluff body.
 11. An apparatus for generatingelectric current, according to claim comprising: a pivot; a bluff bodycomprising a vortex inducing feature and shaped for when disposed in aflowing fluid with velocity v1 having a predetermined oscillatingmovement of the bluff body in alternating directions about the pivotinduced for resulting in relative motion therebetween; a generatorcoupled between the pivot and bluff body for generating electric currentin response to the relative motion; and a mechanism for varying a shapeof the vortex inducing feature.
 12. An apparatus for generating electriccurrent comprising: a pivot; a three dimensional triangular shaped bluffbody comprising: a first sidewall and a second sidewall coupled togetherat an apex for being directed into the fluid flow; an opening for matingwith the pivot for supporting rotation of the bluff body thereabout; aback wall; a second rounded corner opposite the apex and between thefirst sidewall and the back wall; a third corner opposite the apex andbetween the second sidewall and the back wall, for when disposed in aflowing fluid with velocity v1 resulting in vortex shedding for inducinga predetermined oscillating movement about the pivot for resulting inrelative motion between the pivot and the bluff body; and a generatorcoupled between the pivot and the bluff body for generating electriccurrent in response to the relative motion, wherein the second roundedcorner and the third rounded corner each have diameter d1 and whereinthe bluff body is displaced approximately 1.7 times d1 in a directionperpendicular to the fluid flow.
 13. The apparatus according to claim 12wherein the bluff body oscillates in response to fluid flow within arange of fluid flow rates.
 14. The apparatus according to claim 12wherein the apparatus includes other than a feedback system formodifying the predetermined oscillating movement of the bluff body. 15.The apparatus according to claim 12 for in use within a fluid flowhaving a flow rate v1, oscillating in equilibrium within the fluid flow.16. An apparatus for generating electric current, according to claimcomprising: a pivot; a three dimensional triangular shaped bluff bodycomprising: a first sidewall and a second sidewall coupled together atan apex for being directed into the fluid flow; an opening for matingwith the pivot for supporting rotation of the bluff body thereabout; aback wall; a second rounded corner opposite the apex and between thefirst sidewall and the back wall; a third corner opposite the apex andbetween the second sidewall and the back wall, for when disposed in aflowing fluid with velocity v1 resulting in vortex shedding for inducinga predetermined oscillating movement about the pivot for resulting inrelative motion between the pivot and the bluff body; a generatorcoupled between the pivot and the bluff body for generating electriccurrent in response to the relative motion; and a mechanism for varyinga shape of the second and third rounded corners.